Photoprinting article

ABSTRACT

A photographic master is disclosed wherein the master comprises a base of a transparent sheet, a plurality of upstanding configurations of exposed photographic emulsion material spaced in a predetermined pattern on the base, and a protective coating over the upstanding configurations and base to thereby provide a gas escapement means when the master is used to provide a pattern upon a metallic sheet in a contact printing process. An improved photoprinting process and a method for making the master are also disclosed.

United States Patent 1 Detrick et a].

[ Apr. 2, 1974 PHOTOPRINTING ARTICLE [73] Assignee: GTE SylvaniaIncorporated, Seneca I Falls,N.Y.

22 Filed: Feb. 3, 1972 21 App1.No.:223,32l

' [56] References Cited UNITED STATES PATENTS 3,615,468 10/1971 Tiala..96/36.3

3,519,348 7/1970 McLaughlin 96/383 Primary Examiner-Robert P. GreinerAttorney, Agent, or Firm-Norman J. OMalley; Donald R. Castle; William H.McNeill [57] ABSTRACT A photographic master is disclosed wherein themaster comprises a base of a transparent sheet, a plurality ofupstanding configurations of exposed photographic emulsion materialspaced in a predetermined pattern on the base, and a protective coatingover the upstanding configurations and base to thereby provide a gasescapement means when the master is used to provide a pattern upon ametallic sheet in a contact printing process. An improved photoprintingprocess and a method for making the master are also disclosed.

2 Claims, No Drawings 1 PHOTQPRINTING ARTICLE BACKGROUND OF THEINVENTION the metallic sheet, coating the sheet with a lightsensitive orphotoresist material, photoprinting a desired pattern onto the coatedsurfaces by subjecting them to light through a photographic master,removing an exposed or unexposed portion of the photoresist and etchingaway the portions not covered by the resist. In most instances duringthe photoprinting step, the surface of the metallic sheet is coated withthe lightsensitive resist material and is then moved to a stationcontaining the master and stopped when in the desired position. Closecontact between the master and the coated metallic sheet is achieved byapplying a vacuum. Close contact between the metallic sheet and themaster insures that precisely defined patterns are projected on thesensitized material. The metallic sheet is then exposed to actinic lightfor a predetermined period of time while the masters are held in closecontact with the sheet. After a suitable exposure time, the frame isseparated and the metallic sheet is transferred to the etching andfinishing steps.

The photographic masters generally have a photographic emulsion in theform of the desired pattern over a transparent base to achieve asuitable degree of rigidity.

The master, either in the form of a negative or apositive,intermittently contacts the coated sheet. It is also essentialthat the master make essentially flat contact with the metallic sheet toobtain uniform exposure. The vacuum is applied to remove any air pocketsthat are present between the master and the metallic sheet. In order toprevent excessive wear or damage to the emulsion on the master duringthe photoprinting step, a protective coating can be applied to theemulsion'surface.

Ascan be appreciated, the printing step is intermittent in nature. Theother steps of cleaning, etching, resist application and removal can becontinuous. The printing step, therefore, is often a bottleneck in theprocess and a reduction of the time required to accomplish this stepwould constitute a substantial improvement to the photoprinting process.

One particular prior art process utilized to reduce this required timeis disclosed in US. Pat. No. 3,615,468 and assigned to the same assigneeas that of the present Applicants. This process teaches the use of aphotographic master having a solid protective coating over the emulsionon the base of a transparent sheet, this coating containing a pluralityof minute particles. These particles form protrusions in the externalcoating, thereby providing an irregular surface against the metallicsheets. While this process provided an adequate gas escapement meansduring the close contact between master and sheet, these particles,having a degree of hardness greater than that of the metal, occasionallymarred the surface of the sheets. It is believed, therefore, that itwould be an advancement in the art to provide a photographic master andprocess which would enable a substantial reduction in the time requiredto accomplish the printing step while insuring that deformation to thesurface of the metallic sheets will not occur.

Because a new photographic master of this velocity is the end result ofa new and unique method of master production, it is also felt that sucha method would be an advancement in the art.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of thisinvention to provide an improved photoprinting process useful in thecontact printing of thin metallic sheets.

It is another object of this invention to provide a photographic masterwhich substantially reduces the time required to accomplish the printingstep of these meta]- lic sheets while still insuring that deformation tothe surface of the metallic sheets will not occur.

Still another object of this invention is to provide a method for makingthe photographic master.

In accordance with one aspect of this invention there is provided a newmaster in the photoetching process. The master comprises a base of atransparent sheet having at least one essentially planar surface whichdescribes a first plane. Spaced in a predetermined pattern on designatedportions of the planar surface of the base are a plurality of upstandingconfigurations of emulsion material. These configurations and theremaining portions of the base having no emulsion material are coveredwith a solid protective coating, the coating and configurations forminga gas escapement means when the master and the metallic sheet arebrought into contact.

In accordance with another aspect of this invention there is provided anew and unique method for making this master in which a base of atransparent sheet hav ing a coating of unexposed emulsion materialthereon is mated with a standard master and selected portions of theunexposed emulsion are exposed to light to thereby produce a pattern ofexposed emulsion material. The base and emulsion are then subjected to aphotographic developing solution which serves to darken the previouslyexposed portions of emulsion material.

These newly darkened portions are then removed when the base issubjected to a photographic reversing solution, whereupon the base andremaining unexposed emulsion, now in the form of a plurality ofupstanding configurations, are exposed to a light source. Next, the baseand newly exposed configurations of emulsion material are subjected to aphotographic developing solution which darkens the configurations. Theconfigurations are then hardened when the base is subjected to aphotographic hardening solution, after which the base and configurationsare heated for a predetermined period. The final step in producing thisnew master is the application of a solid protective coating which coversthe configurations and portions of the base not occupied by theconfigurations.

A further aspect of this invention provides an improvement to thephotoetching process. understanding of the present invention, togetherwith other and further objects, advantages, and capabilities thereof,reference is made to the following disclosure and appended claims inconnection with the above description of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As previously mentioned, amaster used in the contact printing of a thin metallic sheet must be inessentially flat Contact with the sheet in order to achieve uniformityof the products produced. To achieve this contact, a vacuum is generallyapplied to the printing frame to remove essentially all of the airbetween the master and sheet. Since the degree of contact is generallydirectly related to the vacuum produced in the printing frame, suitablecontact can be calculated on the basis of the vacuum developed. It hasbeen discovered that a master developed in such a manner so as to beprovided with a plurality of upstanding configurations of photographicemulsion material spaced in a predetermined pattern on the base of atransparent sheet and coated with a solid protective coating will form agas escapement means when the master and sheet are in contact. The gasescapement means allows the air trapped in the inner portion of theprinting frame between the sheet and master to rapidly removed and thusreduces the time required to achieve suitable contact as determined bythe degree of vacuum produced.

To produce a new master of this variety has consequently resulted in thedevelopment of a new and unique method for making such masters. Thefirst step in this method involves coating a base of a transparent sheetwith a suitable photographic emulsion. Although any transparentmaterial, such as various plastics, can be used, glass is generallypreferred as a base since it is dimensionally stable particularly underchanging temperature and humidity conditions, as is most often the casein the photoeltching process of metallic sheets.

An emulsion suitable for use in this invention can be derived fromalmost any of the photographic emulsions known in the art. Emulsions ofthis variety, as is well known, usually comprise millions of tinycrystals or grains of a sparingly soluble salt of silver dispersed in awater-permeable binder, usually gelatin.

This emulsion is applied evenly over the surface of the base and is thendried, this drying most usually accomplished by placing the base in adrying oven for an established period of time.

The next step in this method for making the master is to mate the baseand coating with a standard master having a darkened pattern formedthereon. This mating is accomplished simply by placing the emulsioncoating of the base against the darkened patterned surface of thestandard and withdrawing any air present from between the two surfaces.This air withdrawal assures a close contact.

Light is now projected through the standard master and ontocorresponding portions of the emulsion coating not protected by thestandards darkened pattern. The period of the light exposure may rangefrom seconds to 1 minute or more depending on the type of emulsion used.

Upon completion of the light exposure step, the base and emulsion, ofwhich selected portions are now exposed, is subjected to a photographicdeveloping solution for a period of approximately 3.5 minutes, thepurpose of which is to darken the exposed portions of the emulsion. Atypical developer solution which can be utilized in conjunction withthis invention is described on page 372 of Volume of the Encyclopedia ofChemical Technology, Second Edition. A typical formula for such adeveloper is as follows: Elon (p- (methylamino) phenol sulfate), 2.5g;sodium sulfite, 30g; hydroquinone, 2.5g; sodium metaborate tetrahydrate,10g; potassium bromide, 0.5; and water to make 1 liter. Largerquantities are produced by proportionally increasing the individualcomponents of the for mula. Although this developer is suitable for thedeveloping step of this invention, it is understood that this formula isby no means restrictive in that practically any of the many photographicdeveloping solutions known in the art can be used. To prohibit apossible runaway of the developing action created by the developer, thebase is now placed in a tank of stop bath solution for approximately oneminute. This solution is known in the art and comprises a simple formulaof one part acetic acid to 40 parts water.

The next step in preparing the new master is to selectively remove thedarkened exposed portions of the emulsion from the base. This isachieved by subjecting the base to a photographic reversing solution,many of which are known in the art. The base is immersed in a tank ofthis solution for a period of four minutes. A typical formula, given inpercentage by weight, for a reversing solution, and that which ispreferred by applicants, is as follows: Cupric Chloride, 0.5 percent;Citric Acid, 7.5 percent; Urea, 7.5 percent; Commercial hydrogenperoxide (30 percent concentration) 5.0 percent; and the remaining 79.5percent consisting of water. In preparingthis solution, Applicants havefound it preferable to combine the first three components with thewater, after first heating the water to approximately F. The hydrogenperoxide is then added after the solution has cooled sufficiently.

Removal of the darkened exposed portions of emulsion is nowaccomplished, leaving a plurality of upstanding configurations ofunexposed emulsion spaced in a predetermined pattern on the surface ofthe base. These configurations, as will be more adequately explainedwith further description, ultimately determine the pattern to beproduced on the metallic sheets. Many varied patterns in the metallicsheet can be produced, one typical example being an aperture mask for atelevision tube. In this particular example, a sheet having several tinysubstantially similar apertures formed therein is manufactured,consequently necessitating an emulsion pattern of substantially similarupstanding configurations. This is not a stipulation of the procedurehowever, because a pattern of upstanding configurations being dissimilaris also applicable to this type of manufacturing, a typical examplebeing the production of lead frames for integrated circuits in whichseveral varying patterns of circuitry are formed.

With the darkened emulsion now removed, and an unexposed pattern ofupstanding emulsion remaining thereon, the base is now subject to alight exposure. While this exposure is occurring, Applicants have foundit desirable, though not necessary, to place the base under a waterrinse to remove any residue which may have built up as a result of theprevious reversing step. The base is thereafter wiped dry.

To darken the remaining upstanding pattern of emulsion in the base, thebase is immersed in a photographic developing solution similar to thatpreviously described for a period of 5 minutes or more. Runaway of thedeveloping solution is prohibited in much the same manner as alsopreviously described, that being to immerse the base in a stop bathsolution of 1 part acetic acid to 40 parts water. To harden theupstanding configurations of emulsion, the base is next subject to aphotographic hardening solution, several of which are known in the art.A typical formula for such a solution, given by percentage of weight is:Sodium Thiosulfate, 25.0 percent; Sodium Sulfit, 1.6 percent; Aceticacid (30 percent cencentration), 4.7 percent; Cloric acid crystals, 0.7percent; Potassium alum, 1.6 percent; and the remaining 66.4 percentconsisting of water. The base is immersed in the hardener for a periodof two minutes after which it is once again placed under a rinse. Thisrinse, usually water, removes any of the hardener solution still presenton the base. Thorough drying of the base and emulsion is now achieved byplacing the base in a drying oven. Applicants have found that atemperature range of approximately lO0F for a period of one half hour isadequate for this purpose.

The final step in producing the new master is to coat the upstandingconfigurations of exposed emulsion and the portions of the base notoccupied by this emulsion with a solid protective coating. Thecomposition of this aspect of the invention comprises a light sensitive,light hardenable substance, a typical example being polyvinyl alcoholsensitized with ammonium dichromate. Other liquid coatings can be usedif desired, such as epoxy resins, silicones, thin film plastics, and thelike.

When the coating is applied over the configurations and on theunoccupied portions of the base, the end result is that valleys areformed between the configurations. As can be understood, these valleysform a gas escapement means during contact between the master andmetallic sheet in the photoprinting step. On a production line producingtelevision aperture masks from a metal sheet and using a master of theprior art which did not deform the metal surface, the time required toachieve substantially internal contact between master and sheet was inexcess of two minutes. In the master utilizing the coating containingminute projections, the time was reduced to approximately one minute.The new master as developed by the previously described method reducesthis time even further, to approximately 30 seconds, a substantialsaving in production 6 time.

It is also to be noted that in most instances the photographic patternwill be applied to both sides of the metal sheet, the designs being inregister with one another so that etching can be accomplished on bothsides of the sheet. Generally, the same procedure will be utilized inproducing both masters when the above method is used, since thephotostations are essentially duplicates on each side of the sheet. Whenthis method is used, in order to achieve maximum benefits from thepresent invention, similar masters are used so that the time requiredfor the creation of the vacuum will be essentially similar.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed is:

1. A photographic master useful in the photoetching process wherein saidmaster is brought into contact with a flat metallic sheet having anessentially planar surface, said master comprising:

a base of a transparent sheet having at least one essentially planarsurface that describes a first plane; plurality of upstandingconfigurations of exposed photographic emulsion material, saidconfigurations spaced in a predetermined pattern to thereby occupydesignated portions of said planar surface of said base; and solidprotective coating formed over said plurality of configurations andportions of said planar surface of said base unoccupied by saidconfigurations of said emulsion material, said configurations and saidcoating thereby providing a gas escapement means when said photographicmaster and said flat metallic sheet are in contact.

2. The photographic master according to claim 1 in which said protectivecoating is light sensitive and light hardenable material.

UNITEI? ATES PATENT OFFICE C-ERTIFIOATE OF CORRECTION ueenene. 3301 410Dated April 2, 1974 Inventor) Herry Rodney Detrick and Roland N.Harshbarger It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 4 delete "velocity" and insert variety Column 2, line 62delete "understanding" and insert For a bet'cr understanding Column 3,line 2 2- delete "to rapidly" and insert to be rapidly Column 6, line 2,CLAIM 2 delete "is light" and insert is a light Signed and sealed this1st day of October 1974,

(SEAL) Attest:

MCCOY M. GIBSON JR. Q C, MARSHALL DANN Attesting Officer Commissioner ofPatents mg I y UNITED sfmrrs PATENT OFFICE C-ERTIFIQATE 0F EORREC'HONPatent No. 3,801,410 Dated April Z, 197

Inventofls) Herry Rodney Detrick and Roland N. Harshbarger It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Eolumn 2, line 4 delete "velocity" and insert variety j Column 2, line62-- delete "understanding" and insert For a bettr understanding Column3, line 22- delete to rapidly" and insert to be rapidly Column 6, line2, CLAIM 2 delete "is light" and insert is a light Signed and sealedthis 1st day of October 1974 (SEAL) Attest:

Mc'coY M. GIBSON JR. c, MARSHALL DANN Attesting Officer Commissioner ofPatents

2. The photographic master according to claim 1 in which said protective coating is light sensitive and light hardenable material. 